The present invention relates to control systems which align electrical components for precise placement via pick-and-place machines onto surfaces such as printed circuit boards, hybrid substrates containing circuitry traces, and other carriers of circuit tracings. More specifically, the present invention relates to a non-contact light-based sensor system which precisely determines angular orientation and location (x, y) of components to allow a pick and place machine to correct angular orientation of the component with respect to the pick and place machine's coordinate system for proper placement.
The electronic device assembly industry uses pick and place machines to automatically “pick” components from standardized feeder mechanisms, such as tape reels, and “place” such components upon appropriate carriers such as printed circuit boards. A given printed circuit board may include a large number of such components and thus the automation of component placement upon the printed circuit board is essential for cost effective manufacture. One important aspect of a given pick and place machine is the manner in which component orientation and location are detected prior to placement. Some pick and place machines transport the component to an inspection station where it is imaged by an inspection camera, or the like (i.e. off-head systems). Once imaged, the controller, or other appropriate device, calculates orientation and location information from the component image. One drawback associated with such systems is the added time required to transport the component to the imaging station; to image the component; and to transport the component from the imaging station to the placement location. Another type of pick and place machine uses an “on-head” sensor to essentially image the component while being transported from the component feeder to the placement location. Thus, in contrast to the above example, on-head component inspection systems typically allow higher component throughput and thus lower cost manufacture.
Pick and place machines that incorporate on-head sensors are known. One such device is taught in U.S. Pat. No. 5,278,634 issued to Skunes et al., and assigned to the assignee of the present invention. U.S. Pat. No. 5,278,634 discloses an on-head component detector that uses a single light source to direct illumination at and past a component of interest, which illumination then falls upon a detector. The component fits through a fixed size window in the housing of the Skunes '634 sensor. With the light energized, the component is rotated by a vacuum quill while the width of the shadow cast upon the detector is monitored. The minimum shadow width is registered when the sides of a rectangular component are aligned normally with respect to the detector. Associated electronics, sometimes resident in the pick-and-place machine, compute the desired rotational movement of the nozzle (with knowledge of reference axes of the pick-and-place machine). This allows angular orientation of the component, as well as component position to be determined, and corrected for proper placement.
Other pick-and-place machines employ sensors with multiple light sources in the sensor, to accommodate components of varying sizes.
Although the system taught by Skunes et al. has provided a significant advance to the art of electronic component placement in pick and place machines, an efficient sensor adapted for use with components having a wide range of sizes would provide faster placement and less machine down-time to exchange sensors with different sized windows.